Grid controlled discharge tube



Julyfi, 1937. H.' VAN DER HORST GRID CONTROLLED DISCHARGE TUBE Filed June V15, 1936 Patented July 6 1937 UNITED STATES PATENT OFFICE Hajo Lorens van der Horst, Eindhoven, Netherlands, assigno-r to N. V. Philips Glceilampenfabrieken, Eindhoven,

Netherlands Application June 15, 1936, Serial No. 85,413 In Germany July 19, 1935 Claims.

My invention relates to grid-controlled discharge tubes and more particularly to incandescible-cathode ionic relay tubes having a plurality of control grids.

5 By the term ionic relay tubes as used herein is meant grid-controlled rectifier tubes having a gaseous filling comprising one or more gases, vapors, or a mixture thereof. Such tubes, which are used in relay circuits and also as current converters of different kinds, for instance, rectifiers, frequency-changers, and inverters, do not as a rule operate continuously, and the anode current is not established until after the anode'igniting voltage-which is governed by the grid potential-has been reached. Furthermore, as the grid does not recover its blocking efiect until after the anode current has become zero and the discharge path has become deionized, the origi nally-established anode current cannot be continuously biased as is done with a high-vacuum triode.

When an ionic relay tube is provided with a plurality of control grids there is considerable difiiculty in securing for all the grids the same ignition characteristic curves, i. e. anode ignition voltage-grid potential curve. This is because in both types of grid constructions now used, one grid is arranged nearer the anode than are the remaining grids, i. e. the grids are arranged either successively in the discharge path or concentrically with the larger grids surrounding the smaller ones.

Although it has been proposed to overcome this difiiculty by symmetrically arranging a plurality of equally-dimensioned grid members in an equipotential surface of the electrostatic field set up between the anode and the cathode, such constructions provide very irregular ignition. This is due to the fact that the grid members, similarly to a tubular grid, delimit a plurality of control apertures and thus do not insure a uniform control.

In both types of grid constructions, the igniiion characteristic curves for the various grids, clue to discrepancies in the electrostatic conditions, will not be exactly the same. Such constructions are unsuited for those applications in which it is essential that the ignition characteristic curve of all the grids be exactly the same, for example, in circuit arrangements in which two grids must alternately perform the same function, or in which a relay tube must be biased in an identical manner from two difierent sides.

The object of my invention is to overcome the above draw-backs and to provide an ionic relay tube having a plurality of control grid members whose corresponding ignition characteristic curves are identical.

In accordance with my invention, I provide be-' tween the anode and cathode a grid structure comprising a plurality of equally-dimensioned grid members arranged symmetrically to the axis of the electrostatic field set up between the anode and cathode and comprising portions traversing Y the discharge space between cathode and anode d in an equipotential surface of said field so as to form a single aperture arranged symmetrically with said axis and serving as the only passage for the discharge.

In one embcdimentof my invention, the grid structure has the form of a cylindrical box surrounding the cathode and comprising a plurality of sector-shaped mutually-insulated grid members spaced apart to form radial slots serving as y the only passage for the discharge. I prefer to arrange the box-like grid structure symmetrically to the cathode and axially of the tube, and to locate the anode centrally with and immediately above this structure. To prevent starting of the tube at the normal anode voltages, I make the radial slots of sufiiciently small width, whereas I provide in the structure opposite the anode a central aperture symmetrically circumscribed by the grid members and controlling by its area the ignition characteristic curves of the tube.

In order that my invention may be clearly understood and readily carried into effect I shall describe same more fully by way of example, with reference to the accompanying drawing, in which:

Figure 1 is a partly sectionized side view of an ionic relay tube according to the invention, and

Figure 2 is a sectionized View taken along line 2-4 of Fig. 1.

The ionic relay tube shown in the drawing comprises an envelope I having at its bottom a reentrant portion forming a press 2 and containing a gaseous filling, for instance argon at a r pressure of 0.5 mm. Supported from press 2 by lead-supports 3 and 4 is an incandescible cathode. 5. Centrally disposed above the cathode 5 and supported from press 2 by means of a lead-support l4 provided with one insulating sleeve [6 is a disc-shaped anode 9.

Between the anode 9 and cathode 5 is a boxlike grid structure comprising two-sectorshaped grid members 6 and I supported from press 2 by means of support-leads l2 and I3 respectively, and forming a single aperture in the shape of a radial slot I0 (see Fig. 2) lying in an equipotential surface of the electrostatic field set up between the cathode 5 and anode 9. The slot II] is given a sufficiently small width to prevent the discharge from passing therethrough at the normal anode voltage. The bottom of structure 20 is closed by a screen i5 of insulating material supported from lead supports 3 and 4, whereas the lower edges of the grid members 6 and 1, and the screen 8 are protected from the discharge by a cup-shaped member 15 of mica supported from support 3.

Arranged centrally with respect to the anode 9 and formed half by grid member 6 and half by grid member I is an aperture H which permits the discharge to pass to the anode and whose cross-sectional area governs the ignition characteristic curves of the tube.

Due to the symmetrical arrangement and identical shape of the grid members 6 and I, the ignition characteristic curves of the tubes comprising two grids agree to a marked extent.

I have found, that when the slot H! was given a width of about 0.25 mm. it was impossible to initiate starting of the tube at a normal anode alternating voltage of about volts and that it was necessary to give the central aperture H a diameter of about 5 mm. to enable normal operation of the tube at this anode alternating voltage and with a gas filling of argon at a pressure of 0.5 mm. of mercury.

While I have described my invention in connection with specific application and examples, I do not wish to be limited thereto but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What I claim is:

. 1. An ionic relay tube comprising an envelope, an anode and an incandescible cathode within said envelope and spaced apart to form a discharge path, and a grid structure between said anode and cathode and comprising a plurality of similar grid members insulated from each other and symmetrically cooperating to form a single aperture for the passage of the discharge and interrupting the remainder of the discharge path, the edges of said members bounding said aperture lying substantially in an equipotential surface of the electrostatic field set up between said anode and cathode.

2. An ionic relay tube comprising an envelope, an anode and an incandescible cathode within said envelope and spaced apart to form a discharge path, and a grid structure between said anode and cathode and comprising a plurality of mutually-insulated identical grid members delimiting said discharge path along a curve lying substantially within an equipotential surface of the electrostatic field set up between said anode and cathode, and comprising portions forming a single aperture arranged symmetrically to the axis of said field and allowing the passage of a discharge, said members blocking the remainder of the discharge path.

3. An ionic relay tube comprising an envelope, an anode and an incandescible cathode within said envelope and spaced apart to form a discharge path, and a circular box-like grid structure comprising a plurality of mutually insulated sector-shaped grid members forming for the only pasage of the discharge a single radially-extending aperture arranged symmetrical to the axis of the electrostatic field set up between the anode and cathode, the edges of said members bounding said aperture and delimiting said discharge path lying substantially in an equipotential surface of said field.

4. An ionic relay tube comprising an envelope, an incandescible cathode, a box-like grid structure arranged symmetrically to said cathode and axially of the tube and comprising a plurality of sector-shaped grid members, and an anode arranged above said grid structure and centrally therewith, said grid members having between them, as the only passage for the discharge, a single aperture constituted by radially-extending slots of small width to prevent initiation of the discharge therethrough at the normal anode voltages and a central portion whose size controls the ignition characteristic curve of the tube.

5. An ionic relay tube comprising an envelope, an incandescible cathode, an anode, and a multiple grid structure between said anode and cathode and comprising a plurality of sector-shaped members forming a single aperture as the only passage for the discharge between said anode and cathode, said aperture having a central portion whose area controls the ignition characteristics of the tube, and radially-extending slots of small width to prevent initiation of the discharge therethrough at the normal anode voltages, the edges of said members bounding said central portion lying substantially in an equipotential surface of the electrostatic field set up between said anode and cathode.

HAJO LORENS VAN DER HORST. 

